Adjustment mechanism for valves

ABSTRACT

An apparatus for varying the motion characteristics of a valve typically in an engine includes a rotating member such as a valve crank shaft having a conrod with a sliding pin. The sliding pin is constrained to move along a path in a guide member. The guide member is adjustably attached to the engine, and by adjusting the position of the guide member, the trajectory taken by the pin can be varied. The pin also moves along a path of a pivotally attached rocker arm, the path of the rocker arm being different to the path of the guide member. The difference in the paths causes the rocker arm to pivot, and this in turn causes motion in a valve in contact with the end of the rocker arm. By moving the guide member, the differences in the path of the guide member and rocker arm can be accentuated or minimised, thereby altering the motion characteristics of the rocker arm and in turn the valve. This enables the valve opening duration and/or valve lift to be varied. The valve may be fixed to the end of the valve to allow for desmodromic valve actuation, or the valve may include a spring to keep the valve stem in contact with the rocker arm.  
     In one embodiment the rocker arm has an actuator having contact surfaces on the valve which are of substantially constant diameter, in order for the valve clearance to be kept constant as the rocker arm pivots to open and close the valve.  
     An apparatus for adjusting the valve clearance on the above device, including a valve stem having a thread is also disclosed.

FIELD

[0001] The present invention relates to improvements in engines, such asinternal combustion engines, particularly to the actuation of valves andmost particularly, poppet valves for internal combustion engines.

[0002] The present invention also has application to engines or pumpswhich uses valves.

BACKGROUND

[0003] The available torque from an internal combustion engine islargely dependant on the volumetric efficiency of the engine. Forreciprocating piston engines, this efficiency is a measure of the volumeof atmospheric air drawn into the cylinder/s during an induction stroke,relative to the swept volume of the cylinder/s.

[0004] The valve timing of the reciprocating internal combustion enginehas a significant effect on the volumetric efficiency of the engine atparticular engines speeds. An engine having fixed valve timing, ie afixed crankshaft angle for valve opening before piston at top deadcentre and a fixed crankshaft angle for valve closing beyond top deadcentre, will have a particular engine speed where it operates mostefficiently. At this speed, the fixed synchronisation of the inlet andexhaust valves opening and closing relative to the piston positioncreate the combination giving the most torque.

[0005] Obviously it is desirable to have the most torque possibleavailable over a wide range of engine speeds. To achieve the maximumtorque at high engine speeds, it is desirable to have the valves (inletand exhaust) open for as much piston travel as possible. This gives airmore time to enter and exhaust gases more time to exit the cylinder andtherefore increases volumetric efficiency. However, there are limitingfactors for how much piston travel, or how much of an angle (ofcrankshaft rotation) the inlet and exhaust valves can be kept open. Forexample, increasing the angle that the valves are open increases theangle that both the inlet and exhaust valves are open at the same time,which is called valve overlap. Valve overlap is desirable at high enginespeeds as it increases torque output. However, the same amount of valveoverlap that produces good torque at high engine speeds will cause theengine to run poorly and reduces torque output at low engine speeds.Accordingly, in general, opening the valves earlier and closing themlater improves volumetric efficiency at high engine speed at the expenseof torque at low engine speed. Conversely decreasing valve overlapincreases engine torque at low engine speeds but does not give the bestefficiency at high engine speeds.

[0006] It is therefore desirable to have a mechanism whereby the timingof the valve opening and closing can be adjusted according to parameterssuch as engine speed, in order to optimise the torque across a range ofengine speeds. Further, other parameters, such as for example, throttleposition and which gear is engaged, may be used to vary the timing ofthe opening and closing of the valves.

[0007] Apart from valve timing, there are other factors which areimportant in the operation of reciprocating engine poppet valves.Firstly, just before the valve is opened, the valve actuator shouldaccelerate slowly towards the valve, in order to reduce then eliminatethe clearance between the valve and the actuator or between anyintervening tappet arrangement and the actuator. This is to ensure thatthe valve and actuator do not impact on each other with large velocitiesor forces. The valve then needs to be opened as quickly as possible inorder to facilitate the filling of the cylinder with fresh air and fuelin the case of an intake valve, or empty the cylinder of exhaust gas inthe case of an exhaust valve. Once opened, the valve should be held openfor as long as possible before closing rapidly. The valve should thenreseat as gently as possible and then stay closed until the cyclerepeats. As there should be no radical changes in motion, (excessiveacceleration) of the valve, a substantially sinusoidal motion has beenfound to be acceptable in providing a path for valve movement.

[0008] The actuation of valves and the control of their motion has beenaccomplished in the past by the use of camshafts. Camshafts have aneccentric cam lobe that actuates a valve, wherein the profile of the camlobe determines the motion characteristic of the valve. A problem withthis arrangement is that the camshafts spin rapidly and the valves relyon valve springs to keep them in contact with the outer surface of thecam lobe. As the camshafts spin more rapidly, the valves can leave thesurface of the cam lobe due to inertia. This problem has been addressedin part by increasing the strength of the valve spring, however thismakes opening the valve harder and increases wear on the cam lobesurface.

[0009] Another major problem with camshafts is the inability to changethe lobe shape, making modification of the motion characteristics of thevalve difficult. To modify the valve timing, the camshaft needs to bereplaced or machined, with the result that torque is only optimised overa narrow speed range for a particular cam lobe profile. This is one ofthe reasons that engines that perform well at high speed usually lacktorque in the lower range of engine speeds. Further, as the valvesprings push against the cam lobes as the camshaft rotates, significanttwisting forces are generated along the camshaft, which can result incamshaft breakage.

[0010] There are existing devices that attempt to solve some of theabove problems, however, none are completely satisfactory. One device isa cam shaft having two standard cam lobes for the two inlet valves, anda third cam lobe between the two standard inlet lobes. When the engineis spinning below a certain engine speed, the inlet valves are actuatedby the standard cam lobes. When the engine accelerates over apredetermined engine speed, a pin engages with the valve's actuators,which allows both the valves to be actuated by the third cam lobe, whichhas a different profile suited to high engine speeds, wherein the inletvalves open earlier and stay open longer. A similar mechanism operatesin the exhaust valve camshaft. This system has the disadvantage that itis not possible to vary the valve opening and closing times between thetwo predetermined valve motion characteristics, ie there are only twovalve opening durations available. This results in a marked “step” intorque output from lower rpm to higher rpm and fails to achieve themaximum torque output across the whole range of engine speeds, aseffectively only two specific engine speeds are optimised.

[0011] Another method of varying the valve opening and closing angle iswhere the camshaft speed is not always half the crankshaft speed overparts of a single revolution, but varies according to the engine speed.For example, at low rpm the camshaft may spin at the standard rate ofhalf the crankshaft speed. At higher engine speeds, a mechanism mountedon the camshaft causes the camshaft to spin at lower than half crankspeed while opening the valves and keeping them open, thus ensuring thatthe valves are open over a wider angle than at lower speed. In order tomake up lost time (as the crankshaft must average one revolution forevery two crankshaft revolutions), the camshaft must then spin fasterthan half crank speed for the remainder of the revolution to ensure thatit is in the correct position when it is time for the valves to openagain. This system is obviously less than ideal as a complex mechanismis used to vary the speed of the camshaft with respect to the crankshaftover a single revolution. Further, valve lift cannot be modified as thecam lobe profiles cannot be modified.

[0012] Another disadvantage of most valve actuation means is that theycomprise a cam shaft which opens the valves. Camshafts are difficult tomanufacture, and are subject to wear and breakage.

[0013] It has also been found that the method of adjusting valveclearances between the top of the valve and the valve actuator, forexample rocker arm or cam shaft lobe, has disadvantages, such as theneed for the clearance adjusting mechanism to be on the rocker arm,thereby adding inertia to the rocker arm, or the use of shims which aredifficult to get at under the cam lobes, and require buckets to locatethem, which add to the overall length of the valve assembly andtherefore add to the dimensions of the engine.

SUMMARY OF INVENTION

[0014] It is an object of the present invention to alleviate at leastone disadvantage associated with the prior art.

[0015] To this end, the present invention provides a means for adjustingthe motion characteristics of a valve. The motion characteristics of thevalve include timing, such as the crankshaft's angular location beforethe top dead centre reference angle where the valve opens, duration,such as the angle of crankshaft rotation for which the valve will stayopen, lift or travel the amount of lift of the valve for a givencrankshaft angular location, rate of travel and/or force. In one form,the adjustment is actuated mechanically. In another form, the adjustmentmeans is located between a valve actuation means and the valve.Advantageously, adjusting the motion characteristics of the valve by wayof the present invention, enables selection of engine performancecriteria from a range of predetermined characteristics, together with aselection of the degree to which the criteria is to be performed. Forexample, the adjustment of valve motion characteristics may be selectedin a manner which accentuates engine torque. Or, selection may be madeto accentuate engine fuel economy.

[0016] It may also be desirable to produce a valve actuation means whichproduces an approximate sinusoidal motion of valve lift in relation tocrankshaft rotation and/or which also allows the motion characteristicsof the valve to be varied.

[0017] Usually the valve actuation means includes a rotating member.

[0018] Typically the adjustment means varies the valve opening angle,and/or the valve closing angle and/or the valve lift, eitherindividually or collectively. It has been found that it is advantageousto vary the valve lift and duration, and that while these may be doneseparately, it has been found that it is beneficial to increase valvelift and valve opening duration as engine speed rises.

[0019] Accordingly, it is desirable that the adjustment means varies thevalve opening and closing angle and the valve lift collectively.

[0020] In another form, the invention provides an apparatus foradjusting the motion characteristics of a valve, including adjustmentmeans to adjust the valve motion in accordance with the adjustment meanstravel along a non-straight path.

[0021] In another form, the invention provides an adjustment means foruse in an apparatus for adjusting a motion characteristics of a valvecomprising a plate having a guide path.

[0022] In another form, the invention provides an apparatus foradjusting the motion characteristics of a valve including a first guidepath and a second guide path wherein the motion characteristics of thevalve are determined by differences in shape and/or alignment betweenthe first and second guide paths.

[0023] In another form, the invention provides an apparatus foradjusting the clearance of a valve actuated by a desmodromic valveactuation means including a valve having a threaded end portion.

[0024] In a preferred embodiment, the means for adjusting the motioncharacteristics of the valve include an adjustment member having a guidepath and a pivotally mounted valve actuation member having at least oneguide surface, wherein a pin moves along both the guide path and theguide surface, causing the pivotally mounted actuation member to pivotand move the valve.

[0025] Typically, the pin is driven in a substantially cyclic motion.

[0026] Desirably the guide path of the adjustment member and the guidesurface of the valve actuation member are not collateral over theirentire length, ie there is a difference in the paths such that theydeviate from each other at least over part of their length. Thisdifference in paths produces the movement of the actuation member as thepin travels along both paths. Also, a kinematic inversion of pin andguide is contemplated as an alternative embodiment.

PREFERRED EMBODIMENT

[0027] One or more of the preferred embodiments of the present inventionwill now be described, with reference to the accompanying drawings,wherein:

[0028]FIGS. 1a-1 d show a schematic representation of an adjustmentmechanism in accordance with the present invention in various states ofassembly;

[0029]FIG. 2a shows a schematic side view of the adjustment mechanism ofthe present invention and a prior art valve actuation mechanism;

[0030]FIG. 2b shows a schematic view of a non-desmodromic adjustmentmechanism of the present invention and a prior art valve actuationmechanism.

[0031]FIG. 3 shows an isometric view of part of a first embodiment ofthe adjustment mechanism of the present invention;

[0032]FIG. 4 shows an isometric view of all of the first embodiment ofthe adjustment mechanism of the present invention;

[0033]FIGS. 5a and 5 b show end views of a second embodiment of theadjustment mechanism of the present invention;

[0034]FIGS. 6a and 6 b show end views of the adjustment mechanism shownin FIGS. 5a and 5 b;

[0035]FIG. 7 is a graph of typical extremes of variation in lift andduration of the valves compared with the position of the crankshaft, asvaried by the adjustment mechanism of the present invention;

[0036]FIG. 8 is a first embodiment of a guide plate of the adjustmentmechanism of the present invention;

[0037]FIG. 9 is a second embodiment of the guide plate of the adjustmentmechanism of the present invention;

[0038]FIGS. 10a-10 d are embodiments of rocker arms of adjustmentmechanism of the present invention;

[0039]FIG. 11 is a schematic side view of a first embodiment of a slotof a guide plate of the adjustment mechanism in accordance with thepresent invention;

[0040]FIG. 12 is a schematic side view of a profiled surface of a guideplate of the adjustment mechanism in accordance with the presentinvention;

[0041]FIG. 13 is a schematic side view of a second embodiment of theslot of the guide plate of the adjustment mechanism of the presentinvention;

[0042]FIG. 14 is a schematic representation of the slot of the guideplate of the adjustment mechanism of the present invention;

[0043]FIGS. 15a-15 d are embodiments of a sliding pin of the adjustmentmechanism of the present invention;

[0044]FIGS. 16a-16 d are embodiments of the guide plates of theadjustment mechanism of the present invention;

[0045]FIG. 17a is a first embodiment of a guide plate adjustment meansof the adjustment mechanism of the present invention;

[0046]FIG. 17b is a second embodiment of the guide plate adjustmentmeans of the adjustment mechanism of the present invention;

[0047]FIG. 18a is a perspective view of a valve clearance adjustmentmechanism in accordance with the present invention.

[0048]FIG. 18b is an exploded perspective view of the valve clearanceadjustment mechanism shown in FIG. 18a.

[0049] Referring to FIGS. 2a, 2 b, 4, 5 aand 5 b, a mechanism 10 isshown for adjusting the motion characteristics of a poppet valve 1. Themechanism 10 includes an actuation means, for example a valve crankshaft12 having a crank pin 13, which is used to provide the cyclicdisplacement motion and base timing for actuation of the valve 1. Thevalve crankshaft 12 is normally driven by the crankshaft (not shown) byknown means such as a belt, chain drive, or gears, at half thecrankshaft rotation speed. The mechanism 10 is typically mounted in thehead of a reciprocating four stroke engine (not shown) and furtherincludes a pivot point 14 which is fixed to the head of the engine topivotally locate a valve actuator, such as rocker arm 16 which actuatesthe motion of the valve 1. An adjustment member such as guide plate 18is mounted to the head such that it is able to be moved within a rangeof positions, for example a first position 20 and a second position 22as shown in FIGS. 1b, 5 a, 5 b, 6 a, 6 b and 9.

[0050] Crank pin 13 is attached to a conrod 24 through aperture 15 atone end and has a member such as a guide member, for example sliding pin26, at the other end as shown in FIGS. 1a-1 d, 2 and 3. As the valvecrankshaft 12 turns, the conrod 24 moves the sliding pin 26 along aguide, such as path 25 in the guide plate 18. The guide plate 18 doesnot move in response to movement of the sliding pin 26, and the slidingpin 26 is constrained to move along path 25. The sliding pin 26 alsotravels along a guide path 28 in rocker arm 16. There is typically onerocker arm 16 per valve 1, and accordingly there may be two rocker arms16 if two inlet (or exhaust) valves are used per cylinder. The tworocker arms 16 and guide plates 18 can be served by a single conrod 24and sliding pin 26 as shown in FIG. 4, thus actuating two valves (inletor exhaust) simultaneously as in a four valve per cylinder engine head.Obviously the number of valves that can be actuated by a single conrodand/or sliding pin is not limited to two per inlet/exhaust. The path 28may be in the form of a slot having an upper and lower profiled surface,in the case of desmodromic valve actuation, as shown in FIGS. 1a, 1 b, 2a, 4, 5 a, 5 b, 6 a, 6 b, 10 a, 10 c, 13 and 14 or it may be a singleprofiled surface in the case of conventional valve actuation with aspring providing the valve closing force as shown in FIGS. 2b 10 b and10 d.

[0051] In either method of valve actuation described above, the path 25in the guide plate 18 causes the sliding pin 26 to move in a wayconstrained by the profile of the path 25, which causes the rocker arm16 to pivot about pivot point the pivot point 14 which pushes on thevalve 1 via two nuts tightened on the valve stem, as shown in FIGS. 5,18a and 18 b and described later, thus causing valve 1 to open and closeaccording to the differences in the profile of path 25 and path 28. Itis the difference in path profiles as shown in FIGS. 13 and 14 thatcauses the rocker arm 16 to pivot, and the profiles of the paths 28 and25 may be varied according to the motion characteristics desired fromthe valve, which may vary from engine to engine, or with the purpose ofthe engine. Thus the individual path profiles of the guide plate 18 androcker arm 16 are not intended to be limited to the various embodimentsshown in this specification.

[0052] Further, the valve 1 can be replaced by valve system 100 as shownin FIGS. 2a and 2 b, wherein valve system 100 includes a known shim andbucket arrangement that allows the valve clearance to be adjusted, and avalve spring 101 ensures that the valve stays in contact with theactuator 32 when the valve is closing, which may be used innon-desmodromic or conventional valve actuation. The mechanism 10 maysimply replace camshaft 102 as a valve actuation means.

[0053] The assembled parts of the mechanism 10 can be seen in FIGS. 1ato 1 d, wherein the assembly of the conrod 24 to the crankshaft 12 bythe crank pin 13, and the attachment of the guide plate 18 and rockerarm 16 to the sliding pin 26 is shown schematically. A partiallyassembled adjustment mechanism is shown in FIG. 3, wherein the assembledvalve crankshaft 12, conrod 24 and sliding pin 26 are seen inrelationship to the pivot point 14 which is normally in a fixedposition, but can be rotated and includes in this embodiment eccentricsection 11. The assembled mechanism 10 is shown in FIG. 4 wherein twoguide plates 18 are slidingly attached to the eccentric section 11 ofthe rocker shaft 14 and two rocker arms 16 are pivotally attached to thepivot point 14, which would enable the mechanism 10 to operate two inletor exhaust valves. The guide plates, in this case, are constrained toslide linearly by pins (not shown) which fit into guideways 9.

[0054] In operation, the valve crankshaft 12 rotates at half enginecrankshaft speed. The conrod 24 is connected at one end to a crank pin13 on the valve crankshaft 12 and at the other end to the sliding pin26. The pin 26 is located in a guide path 25 of the guide plate 18. Asthe valve crankshaft 12 rotates, the pin 26 is constrained to move alongthe path 25 of the guide plate 18, however the guide plate 18 can movefrom a first position 20 to a second position 22, and any number ofpositions therebetween. The profile of the guide path 25, as shown inthe figures, defines the trajectory of pin 26. The pin 26 also slidesalong path 28 of the rocker arm 16, and the different profile betweenthe path 28 and path 25 causes the rocker arm 16 to pivot back and forthabout pivot point 14. The actuator 32 attached to rocker arm 16 moveswith the arm 16 and contacts the end of valve 1, pushing the valve openand pulling the valve closed. Where non-desmodromic valve actuation isdesired, a valve spring may close the valve 1.

[0055] The position of the guide plate 18 can be varied, in the case ofFIGS. 2a, 2 b, 3 and 4 by rotation of the rocker shaft 14, in a secondembodiment adjustment 1 s due to eccentric adjusting shaft 30 as can beseen in FIGS. 5a, 5 b, 6 a, 6 b 17 a and 17 b. The shaft 30 has aneccentric off-centre lobe 31 which can be turned within aperture 34,thus causing the guide plate 18 to move from a first position 20 whereinthe motion characteristics as shown by line 40 a and 40 b of FIG. 7 suitlow engine speed, to a second position 22, wherein the motioncharacteristics of the valve suit high engine speeds shown by line 42 aand 42 b, also of in FIG. 7. The movement of the guide plate 18 can beseen in the comparison of open valve positions shown in FIGS. 5a and 5b. In FIG. 5a, the adjusting shaft 30 and lobe 31 position the guideplate 18 in the first position 20. In FIG. 5b, the adjusting shaft 30and lobe 31 position the guide plate 18 in the second position 22 andthus the maximum valve opening, as seen in FIG. 5b is greater than themaximum valve position seen in FIG. 5a. The operation of the shaft 30and lobe 31 in the aperture 34 in the guide plate is shown in FIGS. 17aand 17 b and will be described in more detail below.

[0056] The motion characteristics of the valves can be seen in FIG. 7,wherein line 40 a represents the valve lift of an inlet valve (verticalaxis) versus crankshaft rotation angle (horizontal axis) for the valve 1actuated by valve crankshaft 12 while the guide plate 18 is in the firstposition 20. The exhaust valve motion characteristics when the guideplate 18 is in the first position 20 are shown by characteristics whenthe guide plate 18 is in the first position 20 are shown by line 40 b.Line 42 a represents the valve motion characteristics when the guide ofan inlet valve when the guide plate 18 is in the second position 22. Theexhaust valve motion characteristics when the guide plate 18 is in thesecond position 22, can be seen in line 42 b. As can be seen from FIG.7, there is a significant difference between valve lift, valve openingduration and valve overlap when the guide plate 18 moves from a firstposition 20 to a second position 22.

[0057] The reason for the difference in motion characteristics is thatwhen guide plate 18 is in the first position 20, the profile of path 28is positioned such that the differences in the profile between path 25and path 28 are minimised, as can be seen in FIGS. 5a, 6 a and 8 anddiscussed below. This provides a lower valve lift as the pin 26 deflectsless, as shown in the position of pin 26 a in FIG. 8.

[0058] The first position 20 of guide plate 18 opens the valve the leastamount, and over the shortest angle, and is therefore normally used forlow engine speeds where excessive valve overlap is undesirable andincreased turbulence is desirable. The second position 22 of the guideplate 18 is used to generate larger valve overlap and higher lift in thevalves, as seen in the position of the pin 26 b in FIG. 8, and theextension of the valve in FIG. 5b compared to the extension of the valvein FIG. 5a. This arrangement is used during high engine speeds wheremaximum gas flow is required. FIGS. 6a and 6 b show the guide plate 18in the first position 20 and second position 22 respectively, but thevalves in both cases are closed fully, i.e. regardless of the positionof guide plate 18, the valves still close effectively as shown by theequal positions of the valves in FIGS. 6a and 6 b. The difference in thepositions of the plate 18 is clearly seen by the gap between pivot point14 and guide plate 18 in FIG. 6b, whereas in FIG. 6a there is no gap.The mechanism 10 allows the guide plate 18 to be positioned at any pointbetween the first position 20 and the second position 22, thus allowingthe amount of valve overlap and/or the angle of valve opening to beadjusted to any point within the predetermined limits of the valvemotion characteristics. This also provides the advantage of being ableto modify the valve opening angle and/or lift according to any change inthe conditions in order to maximise volumetric efficiency.

[0059] The differences between the profiles of path 25 in guide plate 18and the path 28 in rocker arm 16 are designed to impart the desiredvalve motion characteristics to the valve. For example, when used with arocker arm 16 having a straight path 28, the path 25 shown in FIG. 11,is made up of four portions, each with a specific function. Portion A isa portion whereby, when the sliding pin 26 is in this portion, the valvewill be closed. As the pin 26 travels along the path 25, it moves toportion B, which is a ramp section designed to allow the pin 26 to beginto move at an angle to the direction of motion in portion A. This allowsthe actuator 32 to be brought into contact with the valve (or valveshim) relatively slowly, as there is usually a small gap between the topof the valve assembly and the valve actuator. Once the valve hascontacted the top of the valve, sliding pin 26 enters portion C of path25, where the slope of the path increases greatly and thus causes theactuator to push open the valve quickly. Once the maximum valve openingis approached the sliding pin 26 enters portion D whereby the velocityof the valve while opening is reduced, and the valve starts todecelerate. In portion D, the sliding pin 26 reaches the end of itstravel and the valve crankshaft 12 begins to pull the sliding pin 26back along the portion D in the reverse direction, thus starting toclose the valve again.

[0060]FIG. 12 shows the portions A-D of a profiled surface of a guideplate which uses a spring to return the valve to the closed position,and therefore does not require the lower portion of the path. The shapeof the paths 50 and 51 in FIGS. 11 and 12 respectively are designed tobe used with a rocker arm having a substantially straight path 28.

[0061] If the path of the rocker arm had a shape the same as the shapeof the path of the guide plate, then the rocker arm would not moverelative to the guide plate and accordingly there would be no motion ofthe valve. Therefore there are numerous shapes that either the path ofthe guide plate, or the path of the rocker arm can take in order toproduce the required motion of the valve providing that the other of therocker arm or guide plate has a profile that is different. As anexample, the shape of the path 52 of the guide plate shown in FIG. 13can be used, provided the shape of the rocker arm path 53 differs in thecorrect areas to provide the motion in the rocker arm. This differencein path shapes is shown in FIG. 14 wherein the paths 25 and 28, havebeen overlapped in order to highlight the differences in the profileswhich then cause the rocker arm to deflect and actuate the valve.

[0062] From FIGS. 13 and 14, the differences in the paths in the guideplates and rocker arms can be seen, and the differences relate to valvelift. FIG. 13 relates to path 52 in a guide plate that is adjustedrotatably, for example as shown in FIG. 9. It can be seen that thisarrangement allows a far greater difference between paths 52 and 53, andaccordingly, a far higher valve lift is achieved than in the linearlyadjustable guide plate shown in FIG. 14. This increased valve lift shownin FIG. 13 is accomplished without a radical increase in path deviation,which would be necessary in a linearly adjustable guide plate, such asthat shown in FIG. 8. It is undesirable to have too large a deviation inany of the paths as this may lead to increased wear on the path surfaceswhich will cause the valve motion characteristics to change.

[0063] An advantage of the present system is that by altering thedifferences in the profiles of the paths 25 and 28, it is possible toproduce a valve motion with, for example, a more square top than thatshown in FIG. 7.

[0064] In order to overcome or reduce wear due to high contact pressurebetween the path 28 and the sliding pin 26, it has been found that thesliding pin can be made with a non-circular cross section, called a wearportion, in the region where it travels along the path 28.

[0065] In FIG. 15a, a wear portion 160 is shown having a flat upper andlower surface where the pin contacts a straight path 28. The profile ofthe surfaces varies to match the facing surfaces of the paths. Forexample, the wear surfaces can be flat as in wear surface 160 when usedwith path 128 in rocker arm 116 as shown in FIG. 10a. Alternatively thewear surfaces can be curved with a common centre of curvature as shownby wear surfaces 360 in FIG. 15c to suit a similarly curved path 328 inFIG. 10c of constant radius. If conventional or non-desmodromic valveactuation mechanisms are used, then the sliding pin only needs one wearsurface 260 or 460 as shown in FIGS. 15b and 15 d, as the valve springwill ensure continuous contact of the wear surface with the opposingpath 28 surface.

[0066] It should be noted that the embodiments shown in the FIGS. 10a-10d, 15 a-15 d, and 16 a-16 d, work together in respective sets. A rockerarm 116 having a path 128 as shown in FIG. 10a is used with a gudgeonpin 126 shown in FIG. 15a and a guide plate 118 having a path 125 shownin FIG. 16a. This arrangement forms an adjustment mechanism employingdesmodromic valve actuation wherein the guide plate 118 is adjustedlinearly.

[0067] Similarly, a rocker arm 216 having a path 228 (FIG. 10b) workswith a gudgeon pin 226 (FIG. 15b)and a guide plate 218 having a path 225(FIG. 16b) to form an adjustment mechanism employing a valve to closethe valve, wherein the guide plate 218 is adjusted linearly.

[0068] A rocker arm 316 having a curved path 328 (FIG. 10c) works with agudgeon pin 326 (FIG. 15c) and a guide plate 318 having a path 325 (FIG.16c) to form an adjustment mechanism employing desmodromic valveactuation, wherein the guide plate 318 is adjusted pivotally.

[0069] A rocker arm 416 having a curved path 428 (FIG. 10d) works with agudgeon pin 426 (FIG. 15d) and a guide plate 418 having a path 425 (FIG.16d) to form an adjustment mechanism employing a valve to close thevalve, wherein the guide plate 418 is adjusted pivotally.

[0070] In FIG. 17a embodiments of a mechanism for adjusting the positionof the guide plate 18 is shown. The adjusting shaft 30 is situated inthe aperture 34 in the guide plate 18. By rotating the adjusting shaft30, the eccentric cam lobe 31 on the adjusting shaft 30 causes the guideplate 18 to move linearly, for example, as shown in FIG. 8. The amountof linear movement of the guide plate 18 is determined by the amount ofrotation of the shaft 30. This allows the guide plate 18 to be adjustedto any point between and including the two extreme positions, being thefirst position 20 and the second position 22.

[0071] In FIG. 17b, the shaft 30 is rotatably received in to an aperture134 in a guide plate 618 mounted so as to be pivotally adjustable aboutpoint 135. As the shaft is rotated, eccentric lobes 31 force the guideplate 618 to move. The guide plate is constrained to move pivotally andtherefore, twisting the shaft 30 causes the guide plate 618 to move. Asabove, the amount of movement of the guide plate 618 can be controlledby the rotation of the shaft 30.

[0072] A control means (not shown) is used to control the rotation ofthe shaft 30 for each mechanism 10 which enables the guide plate to bepositioned anywhere between the first position 20 and the secondposition 22. The control means may be a simple device for advancing thevalve opening by twisting the shaft, or any other suitable means formoving the guide plate. Such mechanisms are commonly used to advance theignition timing as engine speed rises. The valve timing in this case maybe adjusted either with or independent of the ignition timing.

[0073] A further embodiment of a guide plate 518 is shown in FIG. 9wherein the guide plate 518 is mounted to a rotatable pivot point 535,so that adjustment of the motion characteristics-of the valve can bemade by rotating pivot point 535 to which the guide plate 518 isattached, to any position between the two positions as shown by thearrow and dotted line, rather than linear motion as shown by the arrowin FIG. 8.

[0074] It should also be understood that the guide plates in any of theembodiments disclosed may be positioned in discrete locations betweenthe first position 20 and the second position 22, for example by the useof a stepper motor. This would allow the position of the guide plates tobe varied in steps according to data from various parameters such asengine speed, rate of change of engine speed, throttle position and gearposition. Accordingly, a fuzzy logic table could be set up to positionthe guide plates in the optimum position for a set of predefinedparameters.

[0075]FIGS. 16a to 16 d show further alternative arrangements for theguide plates. Each guide plate is arranged to be mounted in such a waythat its position is able to be controlled in order for the position ofthe path for the sliding pin to be controlled. In a non-desmodromicarrangement as shown in FIGS. 16b and 16 d, there is no requirement forthe path to be a slot, and as such profiles 125 and 325 can be used, asa spring acting on the valve can be used in a conventional manner toclose the valve and accordingly there will always be pressure on eitherprofile 125 or profile 325 and the underside of the respective rockerarms 118 or 328. This arrangement has the advantage that there is alarge body of knowledge regarding the use of valve springs to close avalve. Also, the reciprocating rocker arms may be made lighter.

[0076] Embodiments of the means for adjusting the position of the guideplate is shown in FIGS. 17a and 17 b. FIG. 17a relates to a method ofproducing linear adjustment in the guide plate using a shaft 30 in anaperture 34 in the guide plate 18. The shaft has a lobe 31 which movesthe guide plate to the desired position when the shaft 30 is turned.Aperture 34 is designed to move the guide plate 18 linearly, andtherefore has substantially straight side walls. As many engines of thetype that use poppet valves have numerous valves in alignment, a singleshaft with multiple lobes 31 can be used to move all the guide plates 18simultaneously.

[0077] A further embodiment is shown in FIG. 17b, wherein the shaft 30is used to cause a rotational motion in the guide plate 18. The twistingof the shaft 30 with eccentric lobe 31 in aperture 134 causes the guideplate to pivot about fixed point 135. If the guide plate is mountedabout a pivot point, as shown in FIG. 9, then the rotation of the shaft30 will cause the guide plate to rotate, and thus increase or decreasethe difference between the paths in the guide plate and rocker arm,which will effect the motion characteristics of the valve. As theaperture 134 is designed to move the guide plate 18 pivotally, side wall136 is longer than side wall 137.

[0078] In the above embodiments, the rocker arm has pivoted while theguide plate has moved either linearly or pivotally. It can be readilydetermined that the rocker arm could also move linearly in response tothe movement of the pin in the path of the guide plate. Further, theguide plate may be fixed in place, and all the adjustment movements cantake place on the rocker arm, eg the rocker arm could have its pivotpoint moveable with respect to the guide plate. This arrangement has theadvantage that the guide plate is then fixed, and all the movement isundertaken by the rocker arm, making the mounting of the guide plategreatly simplified.

[0079] It can be seen from the embodiments disclosed that the movementof the guide plate 18 from its first position to the second positioncauses the sliding pin 26 travelling along path 25 to not only increasethe crank rotation angle across which the valves open, but alsoincreases valve lift at the same time. These aspects in combinationproduce a result that is very desirable, as two of the valvecharacteristics change with only a change in one parameter, that beingthe movement of the guide plate. It is desirable to have the valvesincrease their lift at high engine speeds to ensure that the maximumamount of air enters the cylinder or exhaust gas exits from the cylinderin the time provided. However, at low engine speeds, it has been foundthat increased turbulence in the air entering the cylinder is desirableas it assists in the atomisation of the fuel in the air. When enginesoperate at low speed, the velocity-of the-air-entering the cylinder isalso low, and therefore there is not as much turbulence in the air as itpasses the inlet valves into the cylinder. It has been found thatdecreasing the valve lift and duration increases turbulence andtherefore increases fuel atomisation, which increases torque. At higherengine speeds, the turbulence from the faster air flow providessufficient energy for fuel atomisation, and the limiting factor becomesthe amount of air able to be squeezed into the cylinder. The presentinvention allows for the adjustment of not only the valve openingduration, but also valve lift with only one parameter being adjusted.

[0080] The motion characteristics of the valve may also be varied inaccordance with factors such as throttle position and also which gear isselected.

[0081] It should be noted that it is not essential to increase valvelift and duration with engine speed, and that it may be desirable undercertain circumstances to decrease valve lift and/or durations of theinlet and/or exhaust valve as engine speed increases which the presentinvention is also able to accommodate.

[0082] In FIG. 18a there is shown a guide plate 418 used in desmodromicvalve actuation, having two branches 420, each branch having an actuator32. The actuators 32 sit between an upper flange member 422 and a lowerflange member 424 at the upper end of a valve 1. The valve 1 includes athreaded portion 426, which has a lower nut 425 including the lowerflange member 424 threadedly attached thereto, as shown in FIG. 18b. Anupper nut 428, which is threadedly attached to the threaded portion 426of the valve 1, includes the upper flange member 422. The gap betweenthe upper flange member 422 and the lower flange member 424 may be setby an intermediate shim member (not shown) which would fit between theupper nut 428 and lower nut 425, whereby the size of the shim determinesthe gap between the upper flange member 422 and lower flange member 424.

[0083] In the embodiment shown, the upper flange member 422 includes aspacer 423 which contacts a corresponding spacer 427 on the lower flangemember 424, thus providing the appropriate gap between the flanges.Typically, the size of the gap is slightly larger than the diameter ofthe portions of the actuator 32 that contact the upper and lowerflanges, thereby allowing a clearance between the flanges and theactuators 32. The upper and/or lower nuts may be held in position bylock nuts (not shown). The valve clearance may then be adjusted byremoving the upper lock nut (if provided), removing the upper nut 428having upper flange member 422 and spacer 423, and replacing the upperflange member 422 with spacer with another flange member and spacer ofsuitable size, then reattaching the lock nut onto the threaded portionof the valve 1. In this way, the valve clearance can be adjusted to takeinto account any wear in the system, without having to replace the guideplate 418. The spacer 423 may be integral with or separate to the upperflange member 422, and the lower flange member 424 may also be replacedif desired.

[0084] Alternatively, the upper nut 428 and upper flange member 422 maybe locked into position by the upper nut 428, and the gap between theupper and lower flanges can be set by the position in which the uppernut 428 and flange member 422 are set.

[0085] It is important that the contact surfaces of actuator 32 be ofconstant radius, as in this way the valve clearance will be constant asthe valve is opened and closed, and the rocker arm 16 moves about pivotpoint 14.

The claims defining the invention are as follows:
 1. An apparatus foradjusting the motion characteristics of a valve over a range of openingand closing angles including a member in communication with a valveactuator, wherein the member travels along a non-straight path in aguide, and the position of the guide is varied to adjust the directionof motion of the member.
 2. The apparatus of claim 1 wherein the valveactuator is a pivotally located arm.
 3. The apparatus of claims 1 or 2wherein the guide includes a plate having a non-straight path.
 4. Theapparatus of any one of claims 1 to 3, wherein at least 3 differentopening and closing angles are able to be selected over a range ofengine speed.
 5. An apparatus for adjusting the motion characteristicsof a valve, including adjustment means to adjust the valve motionincluding an adjustment member and a guide member, the guide membermoving along a first guide path in the adjustment member and along asecond guide path in a valve actuator, wherein the first guide path andthe second guide path are not collinear, and the guide member movingalong the first and second guide paths causes the valve actuator to moverelative to the adjustment member due to the differences in these paths.6. An apparatus as claimed in claim 5, wherein the valve actuatorincludes a rocker arm rotatably mounted around a point, the adjustmentmember includes a guide plate adjustable in relation to that point, andan actuation means for moving the guide member along the second guidepath in the rocker arm and the first guide path in the guide platewherein differences in the first and second guide paths are reduced whenthe guide plate is in a first position, compared to the differences inthe guide paths when the guide plate is in a second position. 7.Apparatus for adjusting the motion characteristics of a valve includingan adjustment means having a plate having a guide path.
 8. The apparatusof claim 7 including a valve actuator having a guide path different fromthe guide path of the adjustment means.
 9. The apparatus of claim 8,wherein the amount of non-alignment of the guide path of the adjustmentmeans and the guide path of the valve actuator determines the motioncharacteristics of the valve actuator.
 10. The apparatus of claim 9,wherein varying the position of the adjustment means changes thealignment between the guide path of the adjustment means and the guidepath of the valve actuator thus adjusting the motion characteristics ofthe valve.
 11. An apparatus for adjusting the motion characteristics ofa valve including a first guide path and a second guide path wherein themotion characteristics of the valve are determined by differences inshape and/or alignment between the first and second guide paths.
 12. Theapparatus of claim 11, wherein the first guide path is located in anadjustment member, which moves relative to a valve actuator to alter thedifferences between the shape and/or alignment of the first and secondguide paths.
 13. An apparatus for adjusting the motion characteristicsof a valve including an adjustment means operatively situated between avalve actuation means and the valve, having an adjustment member with aguide path adapted to receive a guide member, the adjustment memberbeing moveable between a first position and a second position, whereinthe guide member travelling along the guide path of the adjustmentmember has a different trajectory when the adjustment member is in thefirst position than when the adjustment member is in the secondposition.
 14. The apparatus of claim 13 wherein the valve actuationmeans includes the means for determining the base timing of the valveactuation.
 15. The apparatus of claim 13 or 14 where the guide membermoves cyclicly.
 16. The apparatus of any one of claims 13 to 15 wherethe position of the adjustment member can be varied over a given rangeof engine speeds.
 17. The apparatus of any one of claims 13 to 16 wherethe position of the adjustment member can be varied over a given rangeof engine loads.
 18. An apparatus for adjusting the motioncharacteristics of a valve including an adjustment member having a firstguide path, a valve actuator having a second guide path, wherein theadjustment member moves relative to the valve actuator, thus modifyingthe motion of the guide member moving along the first and second guidepaths which also modifies the motion of the guide element.
 19. Theapparatus of claim 18 wherein the adjustment member and valve actuatorinclude plates.
 20. The apparatus of any one of the preceding claimswherein an adjustment mechanism does not have its base timing varied.21. The apparatus of any of claims 13 to 15 wherein the guide element ispivotally located.
 22. The apparatus of any one of the preceding claimswherein the adjustment member is slidably located with respect to thepivot point of the guide element.
 23. The apparatus of any one of thepreceding claims, wherein the motion characteristics of an inlet valveare variable independently of the motion characteristics of the exhaustvalve.